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Operation

 

3-3

 

3.5

Switching considerations 

 

Signals passing through the Model 7038 Multiplexer Card
are subject to various effects that can influence their charac-
teristics. The following paragraphs discuss some of these ef-
fects and ways to minimize them. 

 

3.5.1 Card characteristics

 

Insertion loss

 

Insertion loss indicates signal power lost while passing
through the card. This loss occurs in the various signal path
components through the card (connectors, PC board traces,
and relays). The amount of power lost will, of course, depend
on the particular insertion loss specification as well as the ap-
plied power. For example, with an insertion loss of 1dB, and
a 10W source signal applied to the card, about 2W will be
dissipated in the card, and approximately 8W will appear at
the load. Note that, as with most transmission lines, Model
7038 insertion loss values increase with increasing
frequency.

 

Crosstalk

 

Crosstalk figures indicate the amount of signal leakage be-
tween channels or switches on the card. With similar power
levels applied to the various channels, crosstalk will be of lit-
tle consequence. With widely different power levels, howev-
er, crosstalk may produce undesired results. For example,
assume that 10W is applied to channel 1, and 1mW is applied
to channel 2. Assuming a -60dB crosstalk figure, the unwant-
ed signal coupled from channel 1 to channel 2 will be only
20dB below the desired channel 2 signal.

 

VSWR

 

The term VSWR (Voltage Standing Wave Ratio) is defined as
the ratio of the maximum and minimum voltages along a
transmission path, and it indicates the degree of impedance
mismatch. In a perfectly matched system, the VSWR is 1:1,
while open and shorted paths have infinite VSWR values.
Since VSWR is related to both the return loss and reflection
coefficient, VSWR figures indicate the degree of signal loss
and reflection; the lower the VSWR figure, the less signal at-
tenuation that occurs along the transmission path.

 

Isolation resistance

 

The isolation resistance is simply the equivalent resistance
between two given connecting points on the card and is of
importance primarily for DC and low-frequency AC signals
switched  by  the  card.   The  effects  of   this   characteristic

depend on the particular isolation specification. Center-to-
shield isolation resistance, for example, may cause loading
problems with signals having high source resistance.
Channel-to-channel isolation resistance may result in
leakage currents generated in one channel caused by a
voltage source connected to another channel.

 

3.5.2 Cable characteristics

 

Characteristic impedance (Z

 

O

 

)

 

Characteristic impedance is the value of cable impedance
obtained by an RF measurement at either end. For example,
a cable with a 75

 

 

 characteristic impedance is 

 per unit

length. (The characteristic impedance of a cable depends on
the relative diameters of the inner and outer conductors, as
well as on the dielectric constant of the insulating material.)
Since the Model 7038 is designed to work with 75

 

 

 cables,

you must use 75

 

 

 cables to assure proper impedance match-

ing (RG-179 recommended). Mismatching anywhere along
the transmission path will increase VSWR and signal reflec-
tions, decrease return loss, and consequently result in signal
attenuation.

 

Cable attenuation

 

Cable attenuation is analogous to insertion loss of the card it-
self in that it defines the degree of attenuation of the signal as
it passes through the cable. Cable attenuation factors are gen-
erally given in dB per 100 ft. and generally increase with ris-
ing frequency. For optimum performance, choose a high-
quality 75

 

 

 cable with a minimal insertion loss.

 

Cable termination

 

Proper cable termination is imperative to ensure maximum
signal transfer and to minimize VSWR and signal reflec-
tions. In the case of Model 7038 operation, both source and
load impedances should be as close to 75

 

 

 as possible to as-

sure optimum matching and thus maximum power transfer.
For example, if a 75

 

 

 cable is terminated with 150

 

 

, the re-

flection coefficient is 0.33, the VSWR increases to 2, and the
return loss is reduced to less than -10dB.

 

Cable connectors and adapters

 

Although miniature SMB connectors are optimized for best
performance, some small impedance mismatch at connect-
ing points is virtually inevitable. For that reason, it is consid-
ered good practice to minimize the number of connectors
used in a transmission path, especially at higher frequencies.
Where possible, avoid using adapters to convert between
various connector types.

L

C

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Summary of Contents for 7038

Page 1: ...c i a n sw i t ho v e r 1 5 0y e a r so f s p e c i a l i z a t i o n 9 0d a yw a r r a n t y 5d a yr i g h t o f r e t u r no na l l e q u i p me n t 1 3y e a r w a r r a n t i e sf o r n e wa n d p...

Page 2: ...Instruction Manual Model 7038 75 2GHz Multiplexer Card Contains Operating and Servicing Information 7038 901 01 Rev A 6 98...

Page 3: ...LAR USE THE REMEDIES PROVIDED HEREIN ARE BUYER S SOLE AND EXCLUSIVE REMEDIES NEITHER KEITHLEY INSTRUMENTS INC NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT INDI RECT SPECIAL INCIDENTAL OR CO...

Page 4: ...Model 7038 75 2GHz Multiplexer Card Instruction Manual 1998 Keithley Instruments Inc All rights reserved Cleveland Ohio U S A First Printing June 1998 Document Number 7038 901 01 Rev A...

Page 5: ...orporate immediately into the manual Addenda are num bered sequentially When a new Revision is created all Addenda associated with the previous Revision of the manual are incorporated into the new Rev...

Page 6: ...voltage is present in any unknown circuit before measuring Users of this product must be protected from electric shock at all times The responsible body must ensure that users are prevented access and...

Page 7: ...result in personal injury or death Always read the associated infor mation very carefully before performing the indicated procedure The CAUTION heading in a manual explains hazards that could damage...

Page 8: ...CONTACT RESISTANCE 1 CONTACT LIFE 3 105 closures 24VDC 10mA DC 1 105 closures 10W 1 2GHz signal 5 106 closures cold switching AC PERFORMANCE 10 100 500 900 2 For ZL ZS 75 MHz MHz MHz MHz GHz Insertion...

Page 9: ...mplified schematic 2 1 2 3 2 Card configuration 2 1 2 3 3 Input output connecting cables 2 3 2 3 4 Typical connecting scheme 2 3 2 4 Card installation and removal 2 4 2 4 1 Card installation 2 4 2 4 2...

Page 10: ...istance tests 4 2 4 3 5 Channel isolation tests 4 2 4 3 6 Special handling of static sensitive devices 4 7 4 4 Principles of operation 4 7 4 4 1 Block diagram 4 7 4 4 2 Relay control 4 7 4 4 3 Switchi...

Page 11: ...Operation Figure 3 1 T connector multiplexer expansion 3 4 Figure 3 2 4 4 matrix multiplexer connections 3 4 Figure 3 3 1 8 multiplexer configuration 3 5 4 Servicing Figure 4 1 Connections for insert...

Page 12: ...nded verification equipment 4 2 Table 4 2 Insertion loss values 4 2 Table 4 3 Recommended troubleshooting equipment 4 8 Table 4 4 Troubleshooting procedure 4 8 5 Replaceable Parts Table 5 1 Model 7038...

Page 13: ...ng the card for repair be sure to fill out and in clude the service form at the back of this manual in order to provide the repair facility with the necessary information 1 4 Manual addenda Any improv...

Page 14: ...s as ordered 2 SMB 10 jumpers CA 193 1A 1 8 Instruction manual If an additional Model 7038 Instruction Manual is required order the manual package Keithley part number 7038 901 00 The manual package i...

Page 15: ...aces components or connector insulators Operate the card in a clean environment If the card be comes contaminated it should be thoroughly cleaned as explained in Section 4 2 3 Connections This paragra...

Page 16: ...configuration Mini SMB Connector Configuration HI LO Signal Common IN1 IN2 IN3 IN4 OUTA Multiplexer A IN5 IN6 IN7 IN8 OUTB Multiplexer B IN9 IN10 IN11 IN12 OUTC Multiplexer C Multiplexer C Output Mul...

Page 17: ...ee Switching considerations in Section 3 for more information 2 3 4 Typical connecting scheme Figure 2 3 shows a typical connecting scheme for the Model 7038 In this arrangement sources are connected...

Page 18: ...me WARNING Turn off power to all instrumentation including the Model 7001 7002 and disconnect all line cords Make sure all power is removed and any stored energy in external circuitry is discharged 1...

Page 19: ...G Turn off power to all instrumentation including the Model 7001 7002 and disconnect all line cords Make sure all power is removed and any stored energy in external circuitry is discharged 1 Pull out...

Page 20: ...bank B channels 5 to 8 Multiplexer bank C channels 9 through 12 NOTE On power up the Model 7001 display will not show that channels 1 5 and 9 are nor mally closed If the instrument is to be op erated...

Page 21: ...2 12 Note that channels are scanned in the order they appear in the scan list To perform a manual scan first select the RESET default conditions in the SAVESETUP selection of the main MENU Press STEP...

Page 22: ...s switched by the card The effects of this characteristic depend on the particular isolation specification Center to shield isolation resistance for example may cause loading problems with signals hav...

Page 23: ...together using short coaxial cables while the remaining output is connected to one of the other multiplexer bank inputs Note that this connection scheme effectively forms a 4 4 matrix with a 4 input m...

Page 24: ...tput Note that IN11 and IN12 are not used with this configuration Aside from providing a 1 8 mux there are a couple other advantages to using this configuration For one thing the characteristic impede...

Page 25: ...not touch areas adjacent to electrical contacts When servicing the card wear clean cotton gloves Do not store or operate the card in an environment where dust could settle on the circuit board Use dr...

Page 26: ...re the signal output cable is connected to the cor rect output jack Close only the channel being tested Verify that the insertion loss values at the various fre quencies are within the limits stated i...

Page 27: ...7 Turn on the Model 6517A voltage source and allow the reading to settle 8 Verify that the Model 6517A resistance reading is 100M 9 Turn off the voltage source and open channel 1 10 Repeat the proced...

Page 28: ...l isolation tests WARNING NO INTERNAL OPERATOR SERVICABLE PARTS SERVICE BY QUALIFIED PERSONNEL ONLY WARNING NO INTERNAL OPERATOR SERVICABLE PARTS SERVICE BY QUALIFIED PERSONNEL ONLY CAUTION FOR CONTIN...

Page 29: ...odel 7038 WARNING NO INTERNAL OPERATOR SERVICABLE PARTS SERVICE BY QUALIFIED PERSONNEL ONLY WARNING NO INTERNAL OPERATOR SERVICABLE PARTS SERVICE BY QUALIFIED PERSONNEL ONLY CAUTION FOR CONTINUED PROT...

Page 30: ...GAINST FIRE HAZARD REPLACE FUSE WITH SAME TYPE AND RATING CAUTION FOR CONTINUED PROTECTION AGAINST FIRE HAZARD REPLACE FUSE WITH SAME TYPE AND RATING INPUT 250V PEAK LINE RATING 50 60HZ 50VA MAX AC ON...

Page 31: ...o the bench or table Use only anti static type de soldering tools and grounded tip soldering irons 4 4 Principles of operation The following paragraphs discuss the basic Model 7038 op erating principl...

Page 32: ...105 perform this function The output enable OE lines of U101 U102 and U103 are controlled by the power up power down safeguard circuit located in the mainframe This circuit assures that no card relays...

Page 33: ...de the following information Card model number 7038 Card serial number Part description Circuit description if applicable Keithley part number 5 4 Factory service If the card is to be returned to Keit...

Page 34: ...108 RELAY HI FREQ RM2 5V RL 212 P2001 CONNECTOR 32 PIN 2 ROWS CS 775 1 Q100 Q102 Q104 TRANS NPN MMBT3904 TG 238 Q101 Q103 Q105 P CHANNEL ENHANCEMENT POWER FET TG 362 R100 R102 R103 R105 R106 R108 RES...

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Page 39: ...2 Instruction manual 1 2 Input output connecting cables 2 3 Introduction 1 1 2 1 3 1 4 1 5 1 Isolation resistance tests 4 2 M Manual addenda 1 1 Matrix expansion 3 4 Multiplexer expansion 3 4 O Operat...

Page 40: ...nstable Will not read applied input Overload Calibration only Certi cate of calibration required Data required attach any additional sheets as necessary Show a block diagram of your measurement system...

Page 41: ...Keithley Instruments Inc 28775 Aurora Road Cleveland Ohio 44139 Printed in the U S A...

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